Combustion Period Research Articles

Effects of inversed-delta injection rate on late combustion and soot emissions from diesel combustion in a constant-volume chamber

The aim of this study is to clarify the effect of an inversed-delta injection rate, which is a ramp-down injection rate achieved with a tandem injector, on the late combustion period, which affects thermal efficiency and soot emissions. Diesel combustion was simulated in a constant-volume chamber combined with a rapid compression machine. Two types of injection rate profile, namely rectangular and ramp-down, were tested in our experimental trials. To eliminate the significant effect of the maximum injection rate on mixture formation, we compared the results for the two types of injection rate profile under a given rail pressure. The time histories of the heat release rate demonstrated that the ramp-down fuel injection profile shortened the late combustion period by 0.2 ms. As a result, combustion was maintained despite the longer injection duration. The non-dimensional fuel consumption rate, defined in terms of the heat release rate and the fuel injection rate, revealed that high fuel consumption in the injection period reduced the quantity of fuel carried over to the late combustion period, resulting in a short duration of late combustion. When the ramp-down injection profile was employed, the temporal variation of total soot (spatially integrated KL factor) exhibited a rapid decrease after the end of injection. This is due to the abundant oxygen in soot regions that originated from the significant quantity of ambient air entrained into the spray during the injection period. This result indicates that ramp-down injection may reduce engine-out soot emissions.

Disentangling the role of prefire vegetation vs. burning conditions on fire severity in a large forest fire in SE Spain

Fire severity is a function of dynamic interactions between vegetation and burning conditions. To understand the factors that control it, accurate methods for estimating prefire vegetation structure and composition as well as fire propagation conditions are required. Here we analyzed the spatial variability of fire severity in a mixed-severity fire (3217 ha) that occurred in southeast Spain (Yeste, Albacete) from 27th July to 1th August 2017, burning mostly a pine woodland, including part of an earlier fire in 1994. Fire severity was estimated using three satellite-based indices derived from the Normalized Burn Ratio (NBR) using Sentinel 2 and Landsat 8 images from the dates before and immediately after fire. The field-based Composite Burn Index (CBI) was used for validation. Prefire vegetation conditions and fuel models were derived from LiDAR metrics and other vegetation data. Fire propagation conditions were estimated based on a fire progression map provided by the Forestry Services of Castilla-La Mancha. In addition, hourly fire weather and aligned (i.e., in the sense of the propagating fire-front) slope and wind speed were calculated for each burning period. Regression models using different spectral fire severity indices and their driving factors were obtained applying Boosted Regression Trees (BRTs). Fire severity was highly predicted by both burning conditions and prefire vegetation (mean adjusted R2 [Adj.R2]: 86% ± 0.04 and 68% ± 0.05 for training and validation sets, respectively). Alone, burning conditions explained more variance than LiDAR metrics and vegetation separately. The single variables that contributed most to the models were the rate of spread of the fire-front, biomass proxies (i.e., Leaf Area Index [LAI] and fraction of Photosynthetically Active Radiation [fPAR]) and understory vegetation (i.e., density of LiDAR points 1–2 m). Higher fire severity occurred in areas burning uphill, with a high rate of spread driven by high velocity winds and under high maximum temperature. Fire severity was high in wooded stands that were heterogeneous in height, composed by scattered and small Pinus halepensis trees, with high and homogeneous understory cover. In contrast, lower fire severity occurred in mature stands dominated by tall Pinus pinaster and Pinus nigra trees. There were strong interactions between vegetation, weather, fire-aligned topography and rate of spread. Because vegetation variables were important drivers of fire severity, even under extreme fire weather conditions, fuel management treatments to limit fire severity and, potentially, fire size should be implemented.

ОЦЕНКА ХАРАКТЕРА МИКРОЦИРКУЛЯТОРНОГО ОТВЕТА НА ЭКСПЕРИМЕНТАЛЬНУЮ ТЕРМИЧЕСКУЮ ТРАВМУ

Burn disease affects the functioning of almost all functional systems, having a negative effect on them due to the development of endotoxicosis and vascular disorders. At the same time, the greatest attention is paid to the shifts that form in the systemic hemodynamics, primarily in the coronary and pulmonary blood flow, which can cause the development and progression of life-threatening conditions. At the same time, the microcirculatory system is also undergoing changes, but these changes have been studied in much less detail. The aim of this research was to study the state of skin microcirculation in healthy and burned rats. The experiment was carried out on 20 adult male Wistar rats divided into two equal groups. The first group of animals (n=10) was a control group (intact), with its representatives there were not any manipulations, except for a single study of the state of microcirculation. Rats of the second (main) group (n=10) were simulated contact thermal burn using their own patented method. The assessment of microcirculation parameters in the main group of animals was carried out by laser Doppler flowmetry on the device "LAKK-M" on the 1st day (2-3 hours after the injury), on the third and tenth days after the burn period. It was found that thermal injury has a negative impact on the microcirculation system, which is seen in a decrease in the intensity of blood flow through small-diameter vessels. This is achieved by reflex vasospasm, reducing the release of nitrogen oxide by endothelial cells and activating precapillary sphincters, and simultaneously activating the shunting ways of cardiac shunt from the arterial directly to the venous channel, bypassing the capillaries. Thus, in the post-thermal period, a compensatory "robbing phenomenon" is realized in the border zone of the burn, which requires pathogenetic correction.

Prediction and prevention of spontaneous combustion of coal from goafs in workface: A case study

Aiming at forecasting and preventing remnant coal spontaneous combustion in goaf, this thesis conducts determination on the spontaneous combustion tendency of coal seam, simultaneous thermogravimetry and differential scanning calorimetry(TG-DSC) analysis on coal samples, optimization on index gas of spontaneous combustion, and division of spontaneous combustion “three zones” with O2 concentration as the indicator. The conclusions are as follows: the spontaneous combustion period of remnant coal is 1–3 months, so the coal seam is easy to spontaneous combustion. CO and C2H4 are selected as the index gas for forecasting spontaneous combustion in No.12 coal seam and No.12-up coal seam because of their regular evolution tendency in concentration changing with coal temperature and easiness in detecting. As to the spontaneous combustion “three zones” divided by O2 concentration, the depth and width of both heat dissipation zone and left side oxidation zone in the goaf is slightly increased when the “Y” type ventilation is adopted, comparing with the “U” type ventilation, and the asphyxiation zone is extended to about 200 m behind the workface. Pressure balance method and ground fissure sealing are proposed for spontaneous combustion prevention and extinction, which offers some practical experiences for adjacent mine or similar coal seam.

Deposition growth of Zr-based MOFs on cerium phenylphosphonate lamella towards enhanced thermal stability and fire safety of polycarbonate

The fabrication of engineering plastics combining high efficiency flame retardancy and thermal resistance are essential for practical applications. A novel halogen-free binary hybrid with lamellar and porous structure, Zr-BDC@CeHPP, was created by hydrothermal reaction, thereafter blended with polycarbonate (PC) to improve its thermostability and fire safety. With 2 wt% Zr-BDC@CeHPP, temperatures under peak decomposition rates (Tmax1 and Tmax2) of PC were increased by 28 and 34 °C under oxidizing atmosphere. Time to reach PHRR (t-PHRR) and time to ignition (TTI) and of PC were effectively prolonged to 145 and 18 s, respectively. In comparison with pure PC, the peak of heat release rate (PHRR), total heat release (THR), peak specific extinction area (PSEA) and total smoke release (TSR) of PC composites were reduced by 45%, 20%, 74% and 18%, respectively. Moreover, the flame retardant PC reached V-0 rating in UL-94 vertical burning test. The results indicated that the hybrid was able to fully utilize the advantages of Zr-BDC and CeHPP. In the ignition and middle periods of combustion, Zr-BDC@CeHPP played roles in delaying and suppressing explosive combustion. In severe combustion stage, Zr-BDC@CeHPP could catalyze the char-forming process and serve as a barrier.

Effect of Impact Load on Concrete Containing Recycled Tire Rubber Aggregate With and Without Fire Exposure

Over one billion tires are disposed into the environment each year and this has become a major environmental issue in the globe. Recycling of these waste tire rubbers in concrete has gained attention from researchers all around the world. In this study, the impact resistance of rubberized concrete exposed to fire is investigated experimentally in the laboratory. For that purpose, sixty specimens were made with five different mixes replacing their sand content partially with different percentages of tire rubber by weight ratios of 0% control, 6%, 12%, 18% and 24%. The water/cement ratio was kept constant at 0.393 in all the mixes. In each mix, fifteen concrete specimens with the size of (150 x 150 x 73) mm were prepared to expose to fire. Every three specimens were gradually exposed to fire for four various durations of (0, 15, 30, and 45) minutes. Each specimen was then tested in a drop-weight impact machine by dropping 2240-gr and 4500-gr hammers from heights of 280 mm and 450 mm. The average impact energy of three identical specimens required for the occurrence of the final fracture was calculated. The investigational results are compared with results of control samples. It is found that the impact energy considerably increased with an increase of the rubber replacement. It is, also, noted that any increase in the burning period of specimens results in a reduction of the impact energy and more early crushing of the rubberized concrete.

Effect of advanced intake valve closing on the thermo-chemical characteristics of the homogeneous combustion in a DME fueled HCCI engine

This numerical study was performed to analyze the thermo-chemical characteristics of homogeneous combustion on the effect of advanced intake valve closing timing in a DME fueled HCCI engine. To achieve this, the engine simulation was performed using the detailed chemical kinetic mechanism, including 453 reactions for dimethyl ether (CH3OCH3), and the modified NOX mechanism was applied to analyze the NOX reaction pathway of the DME combustion. The experimental study was performed to validate the engine analysis using a single cylinder CI engine with the injection timing of BTDC 40 degree and IVC timing of BTDC 128 degree. The injection quantity and pressure were set to 8 mg and 50 MPa at 1500 RPM, respectively. The results of engine performance such as cylinder pressure, cylinder temperature, heat release rate, and IMEP were decreased and the ISFC and ignition delay were increased when the IVC timing was advanced since the overall rates of a chemical reaction and the reaction rate of OH radicals are reduced. Especially, the reduction of CH2OCH2O2H radicals was a very important factor it affects the ignition delay in the low temperature reaction. Consequently, it influences the LTC and HTC reactions and makes a difference in the fuel oxidation rate and combustion reaction. Furthermore, the OH radicals also had the greatest effect to the CO oxidation and NOX production. The CO and NOX emissions were primarily occurred by the forward reactions of HCO + O2 → CO + HO2 and HO2 + NO → NO2 + OH during the combustion period, respectively. The chemical reactivity and CO oxidation reaction were reduced as the fuel mass fraction increased in the low combustion temperature. In addition, the reaction path of NOX emission related to the thermal NOX reaction did not occur due to the low combustion temperature. Thus, the thermo-chemical characteristics of the DME homogeneous combustion of this work suggest that the chemical reaction of fuel oxidation and exhaust emissions are limited as the effect of chemical oxidation rate, reaction rate, and the OH radical depending on the IVC timing changes.

Six-year observations of aerosol optical properties at a southern African grassland savannah site

Atmospheric aerosols have a significant effect on earth's radiative budget, particularly on regional scales. This paper presents a ~6 year, in situ, ground level aerosol scattering and absorption dataset, measured at a background site strategically positioned to enable differentiation of the effect of anthropogenic, population density and open biomass burning activities on a regional scale. Relatively well-defined seasonal and diurnal patterns were observed for all the aerosol optical properties, i.e. scattering coefficient (σ SP ), absorption coefficient (σ AP ), single scattering albedo (ω 0 ) and Ångström exponent of scattering (α SP ). These patterns were explained by considering southern African specific sources and metrological conditions. Using a receptor modelling method (auto-generated source maps) it was found that air masses that had higher σ SP , σ AP and ω 0 , and lower α SP , if compared with the relatively clean background, passed over source regions with significant industrial or other anthropogenic activities, higher population density, re-circulation of polluted air masses and higher open biomass burning frequency. To quantify differences, four source regions were defined, i.e. Karoo, Kalahari, anti-cyclonic recirculation pattern and the industrial hub of South Africa. Air masses that had passed over the Karoo source region represented the cleanest regional background conditions, while air masses that had passed either over the industrial hub and/or the anti-cyclonic recirculation pattern represented the most significant anthropogenically impacted, as indicated by the aerosol optical properties. The ω 0 medians of air masses that had passed over the Karoo (0.80–0.86) were 9, 12 and 7% lower than in air masses that had passed over source regions with the highest ω 0 median, in the warmest/wettest, coldest, and driest, peak open biomass burning periods, respectively. • A six-year, ground level aerosol optical property dataset is presented. • Well-defined seasonal and diurnal patterns were evident for the optical properties. • Auto-generated source maps were used to explain results within a regional context. • Air masses passing over the Karoo region represented the most natural background. • Anthropogenic influences were evident in air masses passing over all other regions.

A Numerical Study to Investigate the Effect of Syngas Composition and Compression Ratio on the Combustion and Emission Characteristics of a Syngas-Fueled HCCI Engine

Abstract The purpose of this work is to investigate syngas composition (of constituents H2, CO, and CO2) and compression ratio (CR) effects on the combustion and emissions characteristics of a syngas-fueled homogenous charge compression ignition (HCCI) engine, which operates in very lean air–fuel mixture conditions for power plant usage. Investigations were conducted using ansys forte cfd package at low (3 bar indicated mean effective pressure (IMEP)) and medium (5 bar IMEP) loads, and the calculated results were compared with the Aceves et al.’s multi-zone HCCI model, using the same chemical kinetics set (Gas Research Institute (GRI)-Mech3.0). All calculations were carried out at maximum brake torque (MBT) conditions by sweeping the air–fuel mixture temperature at intake valve closing (IVC) (TIVC).This study found out that the H2 consumption rate is slightly high in a low-temperature range in the early period of combustion while the CO consumption rate is high in a high-temperature range in the later period of combustion. The results reveal that the change of H2 /CO ratio and inert gas volume fraction according to fuel composition affects combustion, but the TIVC is the dominant factor affecting combustion phasing at MBT conditions. For each fuel and load condition, the TIVC was significantly reduced with the increase of CR (17.1–22.3) to get MBT conditions, which causes to retard combustion phasing and lowers in-cylinder peak temperature. The oxides of nitrogen (NOx) emissions reduced with increasing the CR due to the lowering of the in-cylinder peak temperature.

Thermal efficiency improvement of super-lean burn spark ignition engine by stratified water insulation on piston top surface

In order to improve thermal efficiency of spark ignition engine under super-lean burn conditions (excess air ratio [Formula: see text]), thermal stratification technique by in-cylinder water injection toward piston surface (stratified water insulated combustion architecture), in which low temperature water vapor layer is formed on the surface, is proposed. From the water spray visualization using the optically accessible engine, injected water is distributed near the piston top surface at ignition timing and thermal stratification can be achieved in the case that water injection timing (SOIw) is set at earlier stage of a compression stroke. In addition, heat flux on the piston surface measured at the same time is reduced by water injection. The 0.5-L single-cylinder engine test at λ = 2.0 at a constant ignition timing also shows that water injection at earlier stage of a compression stroke makes it possible to mitigate knock without significant increase in combustion instability. On the other hand, part of water is distributed near the spark plug at ignition timing with the water injection at SOIw = −60 °ATDC, resulting in unstable combustion. In addition, the engine test at λ = 2.0 and water/fuel ratio(W/F) = 18% shows that knock mitigation by water injection enables spark advance and following combustion enhancement. As a result, combustion period becomes short and cooling loss decreases, followed by the 1.0-pt improvement of gross indicated thermal efficiency. Moreover, the engine can be operated at minimum spark advance for best torque by increasing W/F up to 35%. Finally, stratified water insulated combustion architecture concept is applied at λ = 1.9 with a higher compression ratio of 17, showing that water injection at SOIw = −120 °ATDC and W/F = 50% enables minimum spark advance for best torque operation, and remarkably high gross indicated that thermal efficiency of 52.63% can be achieved with a sufficiently low knock level and coefficient of variation of indicated mean effective pressure.

Experimental study on early prediction index gas for spontaneous combustion

ABSTRACT A spontaneous combustion and oxidation simulation experiment involving coal samples from the fully mechanized top coal caving face 2308 of Getting Coal Mine was performed using a self-developed spontaneous combustion test bed. The aim was to determine the production law of spontaneous combustion products in Getting Coal Mine and provide a basis for establishing an early prediction index system for spontaneous combustion in the goaf. The law governing changes in the concentrations of CO, C2H4, and other gases with temperature in the process of coal sample heating was analyzed, and the index gas of coal sample spontaneous combustion was optimized. The experimental results showed that the shortest spontaneous combustion period was 54 days. The coal samples produced CO at a lower temperature. The absolute amount of CO production increased monotonously during the entire oxidation process, but the increase was uneven under different temperature conditions, and there was a sudden temperature point. C2H4 appeared for the first time at 110 °C, increased monotonously from 110 to 163 °C, and then fluctuated after 163 °C. Finally, CO and C2H4 were selected as the main index gases to predict spontaneous coal combustion in Getting coal mine, and C2H6 and C2H4/C2H6 were used as auxiliary index gases.

CFD Simulation of Symbiotic Disaster Arising from Gas Explosion and Spontaneous Combustion in Longwall Mining Gobs

With the increasing of mining depth, the symbiotic disaster of gas and coal spontaneous combustion is gradually increasing. In order to explore the multi-field coupling law of gas and coal spontaneous combustion in the goaf, the numerical simulation method was used to optimize the key parameters and find the best balance between effectively controlling the gas without expanding the danger zone of spontaneous combustion. The results show that, the higher the level of the high-level drainage roadway, the better the drainage effect, but considering the spontaneous combustion period, it is necessary to reasonably calculate the optimal drainage roadway layout position; the buried pipe extraction has good effect on gas control, but it is not conducive to fire prevention.

Investigation on effects of the exhaust emission characteristics of diesel engine fuelled with mahua oil methyl esters and its blends with diesel

Diesel engines are deliberately known for environmental pollution caused by exhaust emissions and are liable for many health issues further more. Emissions of diesel exhaust might lead to cancer, irritate the eyes, affects the nose, throat and lungs. Biodiesel is an eco-friendly and typical alternative fuel which is produced from vegetable oils through transesterification technique. Biodiesel has its own several advantages than the conventional diesel says decreased in carbon monoxide (CO), unburnt hydrocarbon (HC) and particle matter (PM) emissions, and having fuel properties which are similar to conventional diesel for its easier use in diesel engines. The outcomes demonstrated that the production of lesser CO and HC emission using biodiesel. Nevertheless, a minor increment in NOx emission was noticed for mahua oil methyl ester blends. Brake Specific Fuel Consumption (BSFC) for methyl ester blends was raised as compared to diesel. The combustion analysis exhibited a significant rise in combustion pressure and heat release rate with smaller ignition delay and extended combustion period. From the investigation, it could be said that the effects of mahua oil methyl esters and its blends on diesel engine when compared to conventional diesel ultimately minimizes the health effects of biodiesel exhaust exposure.

Feasibility Study of Emission Reduction on Marine Engine with Variation of Emulsified Water Concentration and Turbocharger Compression Ratio

The characteristics of black carbon and nitrogen oxide reduction versus the water content of emulsion fuel were studied by numerical methods, and a method of reducing fuel consumption was achieved by adjusting the turbocharger compression ratio. The results of the combustion period characteristics, versus the three types of emulsion fuel and the turbocharger compression ratios, shows that the combustion period is shortened in the order of CR00 > CR01 > CR02 > CR03, according to the compression ratio of the turbocharger. As the fuel water content increases, the combustion period is shortened in the order of EMDO16 < EMDO13 < EMDO10. The nitrogen oxide and black carbon reduction was because the combustion period increased, with increasing compression ratio, while the combustion period was shortened, with increasing moisture content of emulsion fuel. This also caused is an increase in the combustion pressure and a shortening of the combustion period, due to the expansion of the volume, in turn due to the micro-explosion of water. This may be due to the shortening of the post combustion period and the reduction of black carbon emissions. In addition, combustion was accelerated in the order—CR00 > CR01> CR02> CR03. By optimizing the water content of the emulsion fuel and turbocharger compression ratio, while considering the exhaust emission and combustion state, reduction of the fuel consumption rate and output improvement are shown.

Nanometric particles of high economic value in coal fire region: Opportunities for social improvement

Spontaneous coal combustion in the La Guajira coals was studied for the presence of carbon nanophases (e.g., carbon nanotubes), occurrence of rare earth elements (REEs) in them, and the probable mechanisms for concentration of these rare compounds. For this purpose, various techniques such as scanning electron microscopy (SEM), Field-emission SEM, transmission electron microscopy (TEM), high-resolution TEM, and focused ion beam (FIB) were used. The development and alteration of the nanoparticles by geo-processes during the early modification periods of coal combustion were explored. Certain types of carbon nanophases and REE compounds may constitute nanominerals and ultra-fine particles accumulated in the coal peat. Assemblages of these nanophases (crystalline and amorphous compounds), predominantly the clay-monazite relationship and its connection to tonsteins in the coal combustion zones in the east region of the coal mines studied in this work, indicate that the coal area was subjected to REE concentration. The carbon nanophases contained several potential hazardous elements (PHEs), including, arsenic, bromine, cadmium, chlorine, fluorine, mercury, and other PHEs. While carbon nanotubes have been known to be produced from spontaneous combustion of coal of varying ranks, the present work is the first report on the naturally occurring REEs and carbon nanophases in the Colombian coal mining area.

Significant ultrafine particle emissions from residential solid fuel combustion.

When addressing particulate matter (PM) emissions from residential solid fuel combustion, ultrafine particles are usually merged into PM2.5, while whose mass concentration is applied as the index in evaluating PM pollution as well as assessing PM-induced health risk. This may not effectively represent the risk from ultrafine particles. In this study, we explored ultrafine particle emissions during residential combustion under both laboratory-controlled and real-world rural household conditions. Significant ultrafine particle emissions (i.e. with emission factors between 2×1015 to 2×1016 particles per kg of fuel) are found for both coal and biomass. High emissions of particle mass concentration often occur at the beginning of the combustion (i.e. the first 30min after fire start) while high emissions of particle number concentration occur in a later combustion period (60-150min). Ultrafine particles account for over 90% of the emitted total particle number concentration from 3nm to 10μm. These emissions elevate ultrafine particle number concentration by more than a decade in indoor environment under which household residents are directly exposed. In addition, we show that there is notable inconsistency between reducing PM2.5 mass based emissions and reducing ultrafine particle number based emissions among various control strategies that were proposed for reducing pollution from residential combustion. Both "cleaner" fuels and stoves that are designed to reduce PM2.5 emissions are found to be not necessarily effective in reducing ultrafine particle emissions, even increase their emissions in some cases. These findings indicate that the overlook of ultrafine particle emissions from residential solid fuel combustion can lead to potential health risk to household residents, especially to those vulnerable ones (e.g., the elderly and children) who are more sensitive to indoor air pollution. More attentions are needed on ultrafine particle pollution and its potential health risk in comparison to using the PM mass concentration index alone.

Effects of Sub-Chamber Configuration on Heat Release Rate in a Constant Volume Chamber simulating Lean-burn Natural Gas Engines

<div class="section abstract"><div class="htmlview paragraph">Sub-chamber is a useful device with regard to sustaining stable operation of compressed natural gas (CNG) engines under lean burn conditions. In our previous studies, we applied a sub-chamber injection system to CNG engines, in which a single injector and a spark plug are mounted in a small sub-chamber. The aim of this study is to investigate the effect of the sub-chamber configuration on heat release in the main combustion chamber. 11 types of sub-chamber with different nozzle number, nozzle diameter, and sub-chamber volume were examined under a condition that pressure is 2.3 MPa, and global equivalence ratio is 0.6. When the sub-chamber with smaller nozzles are used, the penetration velocity of burned gas jet increases. In addition, the velocity also increases with an increasing sub-chamber volume. The high-speed penetration of burned gas jet shortens the period of initial flame development. This is because the high-temperature burned gas quickly reaches to side wall of main chamber, and immediately ignites lean mixtures existing in the main chamber. Consequently, combustion duration time until heat release reaches 90 % is also shortened. On the other hand, the velocity difference between the jets from sub-chambers with different nozzle numbers is small. To predict the penetration velocity, we proposed an empirical formula based on the volume, nozzle diameter and nozzle number of sub-chamber. The jet intensity evaluated from the formula shows correlations with duration times of combustion periods as well as penetration velocities of burned gas jets.</div></div>

A Study of Ignition Method for Gas Heat Pump Engine Using Low Temperature Plasma

<div class="section abstract"><div class="htmlview paragraph">Low temperature plasma ignition has been proposed as a new ignition technique as it has features of good wear resistance, low energy release and combustion enhancement. In the authors’ previous study, lean burn limit could be extended by low temperature plasma ignition while a voltage drop during discharge, leading to the transition to arc discharge, was found. In this study, the structure of plug and power supply’s performance with steep voltage rising with time, dV/dt, are examined to investigate the effects on combustion performance. As a result, comparing three power sources of conventional, IES and steep dV/dt, steep dV/dt showed small cycle-to-cycle variation and shorter combustion period, leading to higher peak value of the rate of heat release and better indicated thermal efficiency by relatively 6% and 4% compared to CIC and IES, respectively.</div></div>

Size-fractionated carbonaceous aerosols down to PM0.1 in southern Thailand: Local and long-range transport effects

In this study, size-fractionated particulate matters (PM) down to ultrafine (PM0.1) particles were collected using a cascade air sampler with a PM0.1 stage, in Hat Yai city, Songkhla province, southern Thailand during the year 2018. The particle-bound carbonaceous aerosols (CA) as elemental carbon (EC) and organic carbon (OC) were quantified with the thermal/optical reflectance method following the IMPROVE_TOR protocol. The concentrations of different temperature carbon fractions (OC1-OC4, EC1-EC3 and PyO) in the size-fractionated PM were evaluated to discern OC and EC correlations as well as those between char-EC and soot-EC. The results showed that biomass burning, motor vehicle, and secondary organic aerosols (SOC) all contributed to the size-fractionated PM. The OC/EC ratios ranged from 2.90 to 4.30 over the year, with the ratios of PM2.5-10 being the highest, except during the open biomass burning period. The concentration of CA was found to increase during the pre-monsoon season and had its peak value in the PM0.5-1.0 fraction. The long-range transport of PMs from Indonesia, southwest of Thailand toward southern Thailand became more obvious during the pre-monsoon season. Transported plumes from biomass burning in Indonesia may increase the concentration of OC and EC both in the fine (PM0.5-1.0 and PM1.0-2.5) and coarse (PM2.5-10 and PM>10) fractions. The OC fraction in PM0.1 was also shown to be significantly affected by the transported plumes during the pre-monsoon season. Good OC and EC correlations (R2 = 0.824–0.915) in the fine particle fractions indicated that they had common sources such as fossil fuel combustion. However, the lower and moderate correlations (R2 = 0.093–0.678) among the coarser particles suggesting that they have a more complex pattern of emission sources during the dry and monsoon seasons. This indicates the importance of focusing emission control strategies on different PM particle sizes in southern Thailand.

Droplet combustion behavior of oxidatively degraded methyl laurate and methyl oleate in microgravity

Droplet combustion behavior of degraded and non-degraded fatty acid methyl ester (FAME) were studied under microgravity condition. Accelerated oxidation tests were conducted for methyl laurate (LME) and methyl oleate (OME) as representatives of FAME, and the changes in viscosities and compositions were evaluated. The Rancimat method was employed for oxidizing fuels at 100 °C for 6 or 24 h. The viscosities and compositions were measured with an Ubbelohde viscometer and a gas chromatography-mass spectrometer (GC–MS), respectively. Results showed that various oxidation products were formed only for OME during the oxidation test, and the amounts increased with an increase in the oxidation time. In addition, viscosities of degraded OME were higher than those of non-degraded OME, which would be attributable to the formation of oxidation products. Subsequently, the droplet combustion experiment was performed at 0.1 MPa, 750 °C in CO2-rich atmosphere under microgravity. Droplet combustion behavior was analyzed in terms of evolutions of droplet diameter squared and the instantaneous burning rate. As a result, the instantaneous burning rate of LME maintained almost constant during its combustion period as well as n-decane, which indicates that the behavior of instantaneous burning rate was not influenced by the difference in fuel properties between hydrocarbon and unsaturated FAME. In contrast, the droplet of degraded OME exhibited puffing during the evaporation and combustion periods. This indicates that oxidation products with various volatilities were formed in the degraded fuels, which resulted in puffing. As oxidation proceeded, the release rate of liquid and vapor by puffing decreased owing to the increased viscosity, which causes puffing more frequently. Furthermore, the time of bubble formation increased with an increase in the initial droplet diameter owing to an increase of the heat capacity of the droplet. On the contrary, the time of bubble formation did not vary drastically with the oxidation time, which was probably owing to a limited change in the heat capacity during the oxidation test. This study addresses the droplet burning behavior of LMEs and OMEs with an emphasis on the effects of oxidation.